1. Field of the Invention
The handling of toxic materials, and more particularly, the packaging of low-level radioactive waste for storage until radioactivity decays.
2. Brief Description of the Prior Art
There are a number of different toxic particulates that must be packaged in a way that prevents their dispersion. For example, the salts carried by ordinary water become contaminated with radioactive isotopes when the water is used for purposes such as cooling or washing in nuclear power plants and other facilities handling nuclear materials. Radioactivity generally builds to only a relatively low level of about 50 microcuries per cubic centimeter. But, this is sufficiently toxic so the salts must be removed from the water and stored until radioactivity decays. Present water treatment systems remove the salts from the cooling or other water, and then mix them with an immobilization material to prevent dispersion.
The immobilization material should have a high strength and combustion resistance, low solubility in water and other likely leaching agents, be capable of holding large quantities of waste material, and available at low cost. Many different materials, including polyethylene, paraffin wax, cement, ureaformaldehyde, asphalt, and bitumen and various resins have been either tried or considered. But, none of them have been completely satisfactory. Polyethylene chars easily and does not mix well with waste solids. Wax has low strength and burns easily. Cement will hold only a small quantity of waste. Ureaformaldehyde, asphalt, bitumen and the different resins that have been considered, also have various drawbacks, including brittleness, the tendency to shrink and crack during cooling or drying, and/or the requirement to control sensitive chemical reactions necessary to make the immobilization material a usable solid.
The use of different additives to overcome some of the undesirable properties of an immobilization material has been considered. For example, it has been suggested to add methyl methacrylate, polypropylene, or polystyrene to improve thermal characteristics of polyethylene. But, these additives have the same problems with charring as polyethylene and thus do not substantially improve its capabilities for mixing with dry toxic solids.